1. Field of the Invention
The present invention relates in general to systems utilized for controlling rotating shafts, and in particular to systems which are utilized to minimize twisting loads on rotating shafts.
2. Description of the Prior Art
In many industrial applications it is not uncommon to have a relatively long and flexible drive shaft which is driven by two or more motors (such as electric or hydraulic motors typically). The goal is to synchronize the operation of the motors to avoid "force fights" between the motors. Force fights are conditions under which the motors are acting counter to one another. This typically results from a lack of synchronization in the motors, but also can be due to the mechanical properties of the shaft. For example, when the shaft is relatively long and flexible it is more likely to be subjected to "force fights" between a plurality of motors which are coupled thereto. Force fights are undesirable for a number of reasons. First, they reduce the overall power transfer from the shaft to other mechanical equipment. For example, in aircraft, such as tiltrotor aircraft, it is not uncommon for such a shaft to lose as much as twenty or twenty-five percent of its total power due to force fights. Second, force fights can generate twisting loads on the shaft which can damage or even break the shaft. In general, drive shafts that are subject to force fights are also subject to an increased occurrence of fatigue loads which in general result in part failure.
In the prior art, attempts have been made to better coordinate the operation of the motors which drive the shaft in an effort to minimize or eliminate force fights. These efforts have been only moderately successful. When hydraulic motors are coupled to the drive shaft, a controller has been utilized to individually control a number of electrical hydraulic valves (EHVs). A sensor assembly is utilized to detect excessive twists or the occurrence of force fights. The sensor data is provided as an input to a controller. The controller supplies command signals to the electrical hydraulic valves to moderate the operation of the hydraulic motors, all in a manner which attempts to reduce or minimize twisting loads on the shaft due to force fights from motors which are slightly out of synchronization. One central problem encountered in the prior art is that, in complex mechanical systems with a variety of individual parts, the operating tolerances on the individual parts combine to provide a substantial range of normal operation for the parts. It is difficult for the sensor assembly and controller to accurately measure and rapidly respond to conditions which indicate that undesirable twisting loads are present in the shaft due to force fights between motors.